feat(editors): expose pen settings on note + slide

The note and slide palettes lacked the settings gear the PDF editor has,
so width / pressure / eraser-size+mode / palm-rejection were unreachable
there (the user's 'toolbar 少了很多东西'). Add the gear to both; it opens
the existing rich pen-settings sheet.

flutter analyze: 0 issues.

lib/editor/canvas/pen_slide_screen.dart

@@ -20,6 +20,7 @@ import '../input/pen_input_service.dart';
 import '../input/pressure_curve.dart' show kNaturalPressureGamma;
 import '../layout/viewport_fit.dart';
 import '../pdf/slide_export.dart';
+import '../ui/pen_settings_page.dart';
 import 'pen_canvas.dart';
 import 'pen_palette_widgets.dart';
 import 'pen_stroke.dart';
@@ -439,6 +440,14 @@ class _PenSlideScreenState extends State<PenSlideScreen> {
                   : 'Finger drawing OFF (pen only)',
               onPressed: _toggleFingerDrawing,
             ),
+            ToolButton(
+              icon: Icons.settings_outlined,
+              selected: false,
+              tooltip: 'Pen settings (width, pressure, eraser…)',
+              onPressed: _penConfig != null
+                  ? () => showPenSettingsSheet(context, _penConfig!)
+                  : null,
+            ),
           ],
         ),
       ),